import java.util.Scanner;
public class Main {

    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        Integer x = in.nextInt();
        int y = 0;
        if ( (x % 2)  == 0){
            y = x * (x+1) /2;
        }else{
            y = x* (x-1 +1) /2 + x;
        }
        System.out.println(y);
    }
}
import java.util.Scanner;

public class Main {

    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        Long x = in.nextLong();
        Long sum = x * (x +1 ) /2;
        System.out.print(sum);
    }
}